The activity-dependent mobilization and synaptic targeting of AMPA receptors is an essential step in the expression of synaptic plasticity, regarded as the cellular correlate of learning and memory in the brain. The parallel-fiber-stellate cell (PF-SC) synapse of the cerebellar cortex, a structure essential for motor-control and coordination, exhibits a unique form of synaptic plasticity characterized by the activity-dependent replacement of calcium-permeable AMPARs by calcium-impermeable AMPARs. These two pools of receptors can be distinguished from one another by a simple biophysical assay making it an ideal model system for probing the molecular basis for subunit-specific AMPAR targeting during synaptic plasticity. Furthering our understanding of the molecular mechanisms underlying the trafficking of calciumpermeable AMPARs is immediately relevant to human disease. The regulation of calcium-permeable AMPARs is implicated in a wide range of disease mechanisms including ischemic damage during stroke and excitotoxic damage resulting from epilepsy, amyotrophic lateral sclerosis (ALS) and neuropathic pain. In this proposal, I will test my hypothesis that stargazin, an AMPAR auxiliary subunit is required for subunitspecific trafficking of AMPARs during plasticity at PF-SC synapses. The proposal is divided into two Specific Aims. In Specific Aim 1, 1 will carry out electrophysiological recordings from stargazer mutant mice in order to systematically delineate the role of stargazin in regulating AMPAR surface expression, synaptic targeting and plasticity at cerebellar PF-SC synapses. In Specific Aim 2, 1 will examine the molecular basis for subunit-specific AMPAR trafficking at PF-SC synapses. To this end, I will carry out viral-mediated in vivo gene transfer in stargazer mice as a way of reintroducing both a full-length and a deletion mutant version of stargazin into stellate cells. Such experiments will allow me to zero in on the precise role that stargazing plays in mediating changes in AMPAR subunit composition during plasticity. This would be the first demonstration of subunit specificity in stargazin-mediated targeting during synaptic plasticity. PUBLIC HEALTH RELEVANCE: An essential feature of synaptic plasticity, the mechanism through which neurons in the brain store information, is the exquisite control of a synapse's supply of AMPA receptors. This proposal is directed towards understanding the molecular machinery responsible for AMPA receptor regulation at synapses. In so doing, I hope to provide important insights into pathological states of the brain including stroke, epilepsy, Lou Gehrig's Disease and chronic pain.